Electron beam generator

ABSTRACT

An electron-beam generator comprises a cathode with a thermionic emitter, an anode and an electromagnetic system means; opposite said thermionic emitter there is disposed an additional electrode maintained at a negative potential relative to said anode; the electromagnetic system means establishes a magnetic field with the lines of force thereof curved through an angle close to or exceeding 90*; the cathode, anode, additional electrode and electromagnetic system means are disposed with respect to one another in such a manner as to act upon the electron beam in the direction of the curve of the magnetic field lines and to bend the electron beam in the plane of the magnetic field lines through an angle larger than said angle of curvature of the magnetic field lines by a value close to or exceeding 90*, with the result that in an acceleration area the electron beam travels across, and, upon completion of the acceleration phase, along the lines of force of the magnetic field. The electron-beam generator may be employed in electron-beam furnaces for vacuum heating and melting of metals, as well as in ultra-high frequency instruments and amplifiers wherein the electron beam interacts with the electromagnetic field.

112-Z1-74- OR 398579014 United States Patent 191 Prudkovsky et al.

[ ELECTRON BEAM-GENERATOR [22] Filed: Jan. 2, 1973 21 Appl. No.: 320,678

Related US. Application Data [63] Continuation of Ser. No. 174,771, Aug. 25, 1971,-

[58] Field of Search... 219/121 R, 121 EM,'121 EB; 250/495 Rj 118/491; 13/9, 31

'1 I .1 f 5 2 5 z 1 I I 1 z 1 z I 1 1 I I g i 4 1 Dec. 24, 1974 3,655,903 4/1972 Roman etal. 13/31 Primary Examinerl. V. Truhe Assistant Examiner-G. R. Peterson Attorney, Agent, or Firm-Holman & Stern 1 1 ABSTRACT are disposed with respect to one another in such a manner as to act upon the electron beam in the direcabandoned tion of the curve of the magnetic field lines and to .bend the electron beam in the plane of the magnetic [52] L8. Cl. 219/121 EB, 13/31 1 51 1m. (:1 B23k 15/00 fie hncs' anglelmg'er than angle curvature-of the magnetic field lines by a value close to or exceeding 90, with the result that in an acceleration area the electron beam travels across, and, upon completion of the acceleration phase, along the lines [56] 2 References C'ted of force of the magnetic field. The electron-beam gen- UNITED STATES PATENTS erator may be employed in electron-beam furnaces for 2,994,801 8/1961 Hanks 219/121 EB X vacuum heating and melting of metals, as well as in 3,040,112 '6/ 1962 Smith, Jr 219/121 EBX ultra-high frequency instruments and amplifiers 3,132,198 5/1964 Du B018 6181. 13/9 wherein the electrgn beam interacts with the electro- 3,437,734 4/1969 Roman et a1. 13/31 magnetic fi 3,472,999 10/1969 Yamamoto et a1. 219/121 EB X 3,514,656 Fisk 219/121 EB 8 Claims, 6 Drawing Figures PATENTED BEC24|974 sum 1 or 2 ELECTRON BEAM GENERATOR 'This is a continuation, of application Ser. No. l74,77l, filed Aug. 25, 1971 now abandoned.

FIELD OF THE INVENTION The present invention relates to the field of electronics and, more particularly, to electron beam generators designed to generate very intense electron beams.

One example of application of the invention is in the field of electron bombardment melting and casting of metals in vacuum.

' Another field of application embraces ultra-high frequency-generators and amplifiers wherein the elec tron beam interacts with an electromagnetic field.

In developing the foregoing electron beam generator, it is necessary to solve the problem of accelerating and focusing a given electron beam to counter the spreading effect of the field established by electrons, as well as the problem of maintaining the desired beam configuration on a desired trajectory.

To solve the latter problem useis made of a longitudinal magnetic field which prevents the spreading of an electron beam in a transverse direction provided electrons are supplied into the magnetic field in such a manner as to rule out transversal electron pulsations. In the acceleration zone the space charge effects operating to spread the electron beam are generally counter balanced by the lateral components of the electric field of the system. r

If this equilibrium is upset, the conditions of ingress of electrons into the magnetic field are disturbed thereby-entailing pulsations, which is an inherent drawback of this type of electron beam generators. The magnetic field usually has no part in the formation of the electron beam, for electrons are directed along the magnetic field lines by the forces of an electrostatic field, or else it is absent adjacent the cathode as a result of its magnetic screening.

DESCRIPTION OF PRIOR ART The sole exception to this is the magnetron generator, the most efficient so far. The electrons therein are accelerated by cross-over electric and magnetic fields toward the lateral axis of the source; further the electron beam therein-is directed by an additional electric field along the axis of the source and curved through an angle close to 90.

Yet, magnetron generators are somewhat unstable, as far as pulsations in the electron beam formed therein are concerned; any attempt to maximize the emitting surface will inevitably bring about pulsations. Pulsations arise with the variations in electron beam intensity, voltage and magnitude of the field. I

Several designs of electron beam generators provide for the electron beam to be deflected by a desired angle'.

of curving additional focusing field are called for, which is a definite disadvantage of such generators.

Thus, the adverse feature of the known designs of electron beam generators which prevents raising the intensity of the electron beam and providing stability of electron beam generator operation, mainly consists in electron beam pulsations arising in the longitudinal magnetic field. Neither do the known electron beam generators provide for the curving of intense electron beams through an angle materially larger than with the provision of magnetic focusing after the completion of this curving.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above listed drawbacks.

It is another object of the present invention to provide an electron beam source free from pulsations in the longitudinal magnetic field focused electron beam, and not sensitive to the variations in the intensity of same or in other electric parameters.

To increase the overall current of the electron beam generator and facilitate the operating condition of the emitter, the emitter size (its emitting surface) must be maximized, as far as possible, in relation to the dimensions of the electron beam at the egress from the source.

Further design requirements include the curving of the electron beam through an angle materially in excess of 90, elimination of direct visibility intermediate the egress channelof the electron beam generator and the zone adjacent the cathode thereof, as well as protection of the thermionic emitter from ion bombardment.

The problem is solved by providing an electron beam generator with an additional electrode disposed opposite the thermionic' emitter and having a negative potential relative to the anode, with the lines of force of the magnetic field established by an electromagnetic system in the electron beam acceleration and focusing region curved through an angle close to or exceeding 90; the cathode, anode, additional electrode and electromagnetic system are disposed so as to act upon the electron beam in the direction of the curve of the magnetic field lines and'to provide a curving of the electron beam in the plane of the magnetic field lines by an angle exceeding said angle of curvature of the magnetic field lines by a value close to or exceeding 90, with the result that in the acceleration zone the electron beam moves across, and, upon completion of the acceleration phase, along the magnetic field lines. v

The thermionic emitter, the cathode, anode and additional electrode are preferably toroidal concentrically disposed bodies of revolution, and the magnetic field. lines formred by a cylindrical electromagnetic system coaxial with said thermionic emitter preferably lie in the meridian planes of the system.

Additionally the thermionic emitter preferably has arectilinear elongated configuration, and the cathode,

anode and additional electrode preferably have cylindrical surfaces with the generatrices thereof parallel to said thermionic emitter and perpendicular to the plane of the lines of force of the plane-parallel magnetic field established by the electromagnetic system extended in the same direction as the thermionic emitter.

In certain cases the thermionic emitter is preferably formed as a curvilinear rod, with the cathode, anode, additional electrode and electromagnetic system curved in conformity with the curvature of the thermionic emitter.

The electromagnetic system is preferably provided with a soft-iron screen, and the anode is preferably disposed on one side of the thermionic. emitter.

Additionally, the electron beam generator of this invention is preferably provided with an additional rod maintained at the same potential as that of the anode which forms an emission chamber for the electron beam confined on two sides thereof in the lateral dimension.

The present invention is illustrated as to particular preferred embodiments thereof in the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view illustrating structural details, and configurations of revolution, of a preferred embodiment of the present invention;

' FIG. 2 shows in part a plan view of FIG. 1;

FIG. 3 is an alternative embodiment of the electron beam generator of this invention to form a flat electron beam;

FIG. 4 is a further embodiment of the electron beam generator of thisinvention to form a curvilinear electron beam;

FIG. 5 is a representation ofa version of disposition of the electron beam generator of this invention as employed in a vacuum metal casting furnace;

FIG. 6 is-a representation of the electron beam generator of this invention as may be employed in a ultrahigh frequency instrument.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT It is herein contemplated that there shall be realized the principle of. focusing an electron flow into a small cross-section. Electrons thermionically emitted from the emitters of the present invention are acted upon by the considerable lateral forces of an electric and a magnetic field, largely in excess of space charge effects.

The mentioned forces are counterbalanced by the cent'rifugal forces of inertia arising on curvilinear trajectories. Under such conditions the space charge field effect is the third small force whose variation produces no effect whatever on the movement of electrons, and the electron beam acquires stability. The lines of force of the magnetic field in the electron-beam generator of this invention lie in the place wherein the electron beam is curved. Adjacent the cathode the electron trajectories are directed perpendicularly to the magnetic field lines, just as in magnetron generators, owing to which the magnetic field forces are utilized to the fullest possible extent. As distinct from a magnetron generator, the electron-beam generator of the present invention has magnetic field lines with a pronounced curvilinear geometry. In the event the radius of curvature of the lines of force are compatible with the period of pulsations of the electron beam in the magnetic field, it may be possible to select these values such that the amplitude of pulsations may be attenuated almost to zero over a single period of oscillation. This in effect implies the feasibility ofsupplying the electron beam into the magnetic field which subsequently maintains pulsationfree cross-sectional dimensions. As distinct from magnetron generators, the electron beam is curved by the combined force of an electric and a magnetic field, so

that there may be realized a trajectory having a material curvature and, accordingly, a focusing into a smaller cross-section; the direction of traverse of the electron beam may be varied by an angle materially ex- 5 ceeding 90. This feature allows increasing the perveance of the source by maximizing the emitter disposed in the periphery of the axis-symmetrical system.

Ion bombardment is eliminated; direct visibility of the emitter and the target is easily eliminated, which is of 0 particular utility in the application of the electronbeam generator of this invention in connection with electron bombardment furnaces.

Disposition of the magnetic field lines in the plane of curving of the electron beam permits obtaining, by the completion of the curving, a magnetically focused electron beam in a longitudinal magnetic field.

Considering now the present invention in greater detail, and referring to'FIG. l of the drawings, there will be seen illustrated therein an annular emitter I mounted in the trough about an annular cathode 2 having conical focusing lips. On one side of the cathode coaxially therewith there is disposed a tubular anode 3 having a toroidal surface.

Opposite the annular emitter 1 there is disposed an additional electrode 4 coaxial with the cathode 2 whereto is applied a potential the same as that of the cathode or a negative potential relative to the anode 3. Coaxially with the cathode Z'and anode 3 there is disposed a coil 5 of an electromagnetic system encircled by a soft-iron shield 6. A target 7 is disposed on the axis of the electron-beam generator which the electron beam reaches upon passing through an emission chamber 8.

The magnetic field lines offorce lie in the meridian planes of the electron-beam generator, as indicated by the dot-and-dash lines in FIG. 1 of the drawings.

The electron beam is schematically represented by dotted lines. f v e i The electron-beam generator of this invention operates as follows. v

Electrons thermionically emitted from the annular emitter 1 form a circular electron beam travelling in the zone adjacent the cathode perpendicularly to the lines of force of the magnetic field. A force produced by interaction with the magnetic field and directed along the azimuth imparts to electrons an azimuthal velocity. Interaction of the azimuthal velocity with the magnetic field gives rise to a transverse force increasing with acceleration and exerted in the same direction as the force of the electric field. These forces will be seen to constrain the electron beam to follow highly curved trajectories around, the anode 3 and thence back by 180. In this region the field forces impinging on the beam electrons are counterbalanced by substantial centrifugal forces. Space charge effects prove to be materially lower than those of the external field and unable to materially affect the focusing. This provides for the stability of the electron beam. Disposition of the anode 3 in the vicinity of the emitter 1 will be seen to result in the establishment of an electric field of large magnitude which dissipates the space charge and provides intense emission, whereas centrifugal focusing prevents electrons from reaching the anode 3.

Bending around the anode 3 the electron beam again intersects the magnetic flux in the reverse direction, drops its azimuthal velocity and reverses the sign thereof. At the egress to the rectilinear section there is formed an electron beam of tubular cross-section, with the remaining azimuthal velocities furnishing a magnetic force Sufficient to offset space charge effects. Travelling further, in conformity to the curvature of the magnetic field lines, electrons reach the surface of the target 7. Owing to the poor vacuum inherently present in the system and the heating of component parts due to the intensity of the electron beam, ions formed from ionization of "residual gas and the heated parts are formed into a beam and trapped by the additional annular electrode 4 and thereby'repelled from the cathode zone.

FIG. 3 is a representation of an alternative embodiment of the electron-beam generator of this invention, which provides a flat electron beam. The emitter 1 thereof is shaped as a rectilinear rod. The cathode 2, anode 3 and additional electrode 4 thereof have cylindrical surfaces with the generatrices thereof parallel to the emitter l and perpendicular to the plane of the magnetic field lines. The windings of the coil 5 of the electromagnetic system and the shield 6 thereof will be seen to be extended in the same direction.

FIG. 4 is an illustration of an alternative embodiment of the electron-beam generator of thisinvention which provides a curvilinear electron beam. The emitter 1 thereof is formed as a curvilinear rod, (for example, elliptical) either enclosed or otherwise. The cathode 2, anode 3, additional electrode 4 as well as the windings of the coil 5 of the electromagnetic system with the shield6 thereof are curved in conformity with the curvature of the emitter 1.

FIG. 5 represents an alternative embodiment of the electron-beam generator'of the present invention as employed in anelectron bombardment furnace. The annular emitter l with the cathode 2 and inner anode 3 thereof will be seen to be disposed coaxially with the target, which in this case is a crucible 9 containing a An annular electron beam emitter by the emitter 1 is formed by an electric and a magneticfield established by the electrodes 2 and 4, anode 3 and electromagnetic system 11 with the magnetic circuit 12. Under the action of electric and magnetic forces the electron beam, indicated by the dotted line in the figure, will be seen to be deflected, focused together and passed into the emission chamber 8 disposed above the crucible 9. The magnetic field of the lower solenoid of the electromagnetic system 11 provides for the focusing of the electron beam on the surface of the crucible 9 as well as for the required partial inipingment ofelectrons on the rod 10. The electron beam reaching the surface of the crucible 9 serves to form and maintain a liquid bath of the melt stock. The gaseous products formed in the process are pumped off the open surface. Ion beams arising above the melt stock surface will be seen to be trapped melt stock. The annular emitter 1 may be disposed at I the lever of, above or beneath the crucible 9. FIG. 5 represents aversion whereby the generator electrodes are disposed above the crucible 9. Above the annular emitter 1 there is disposed coaxially therewith an additional annular electrode 4 which furnishes a field to defleet electrons and traps ionbeams emitted by the sur' face of the crucible 9. On the axis of the electron-beam generator interiorly of the anode 3 there is mounted a rod 10 coaxial therewith whose potential is maintained the same as that of the anode 3 or close thereto. The

rod 10 will be seen to provide for the feeding of the melt stock or for the extraction of the crystal formed herein from the melt. The rod 10 plays but a minor role in the focusing of the electron beam and may be thus incorporated into or removed from the design requiring for the purpose only slight modification of the geometry, disposition or potential of the additional electrode 4 by the additional electrode 4 which repels ions from the vicinity of the cathode zone.

FIG. 6 is a representation of an alternative embodiment of the electron-beam generator of this invention in a U.I'I.F.-instrument.

An annular emitter 1 with the cathode electrode 2, inner anode 3 and additional electrode 4 thereof is disposed coaxially with an electromagnetic HF system 13. This system may be a resonance or a periodic system in U.H.F.-instruments. An electromagnetic system 14 with the magnetic circuit 15 thereof, or a permanent magnet, not shown, establishes a magnetic field with the lines of force thereof lying in the meridian planes of the-axis-symmetrical system.

The electron-beam generator of this embodiment operates in the following manner.

vAn annular electron beam emitted by an annular emitter 1 is formed by an electric and a magnetic field established by electrodes 2 and 4, an anode 3 and an electromagnetic system 14 with the magnetic circuit 15 thereof. The electron beam, acted upon by the electric and magnetic forces, will be seen to be deflected, focused together anddirected into an emission chamber 8 wherein it interacts with an electromagnetic HF system l3 thence to reach a collector 16.

What is claimed is:

1. An electron-beam generator, comprising: a cathode with a thermionic emitter and emitting an electronbeam, an anode, an acceleration and shaping region where the electron beam is accelerated and shaped, an

additional electrode disposed opposite said emitter and having a negative potential relative to said anode; an electromagnetic system means for establishing a magnetic field with the lines of force thereof curved through'an angle substantially equal to said cathode, anode, additional electrode and electromagnetic system means being disposed and orientated with respect to one another so as to define field generating means providing a combined electric and magnetic field acting upon the electron beam in the direction of said curve of the magnetic field lines of force for bending the electron beam in a plane of the magnetic field lines through an angle larger than said angle of curvature of the magnetic field lines by a value substantially equal to 90, with the result that in said acceleration and shaping region the electron beam travels across the magnetic field lines of force and upon completion of said acceleration and shaping the electron beam travels along said lines without undesirable transverse pulsatrons.

2. An electron-beam genenrator as claimed in claim 1, wherein said thermionic emitter, cathode, anode and additional electrode are toroidal bodies of revolution disposed concentrically and said electromagnetic system is cylindrical and wherein said lines of force of the magnetic field formed by the cylindrical electromagnetic system means coaxial with said emitter lie in meridian planes.

3. An electron beam generator as claimed in claim 1, wherein said magnetic field includes parallel magnetic field lines, and said thermionic emitter has a rectilinear elongated configuration, and said cathode, anode and additional electrode have cylindrical surfaces whose generatrices thereof are parallel to said emitter and perpendicular to a plane containing the lines of force of said magnetic field lines established by said electromagnetic system means disposed in the same direction as the emitter.

4. An electron-beam generator as claimed in claim 1,

wherein said emitter is formed as a curvilinear rod, and

said cathode, anode, additional electrode and electromagnetic system means have curved shapes in conformity with the curvature of said emitter.

5. An electron-beam generator as claimed in claim 1, wherein said electromagnetic system means is provided with a soft-iron shield.

6. An electron-beam generator as claimed in claim 1, wherein said anode is disposed on one side of said emitter.

7. An electron-beam generator as claimed in claim 1, comprising an additional conductive rod means maintained at a potential the same as that of said anode so as to form an emission chamber confined on two sides thereof in a transverse direction of said rod.

8. An electron-beam generator as claimed in claim 1, wherein said thermionic emitter includes an active surmovement of the accelerated electron beam. 

1. An electron-beam generator, comprising: a cathode with a thermionic emitter and emitting an electron-beam, an anode, an acceleration and shaping region where the electron beam is accelerated and shaped, an additional electrode disposed opposite said emitter and having a negative potential relative to said anode; an electromagnetic system means for establishing a magnetic field with the lines of force thereof curved through an angle substantially equal to 90*, said cathode, anode, additional electrode and electromagnetic system means being disposed and orientated with respect to one another so as to define field generating means providing a combined electric and magnetic field acting upon the electron beam in the direction of said curve of the magnetic field lines of force for bending the electron beam in a plane of the magnetic field lines through an angle larger than said angle of curvature of the magnetic field lines by a value substantially equal to 90*, with the result that in said acceleration and shaping region the electron beam travels across the magnetic field lines of force and upon completion of said acceleration and shaping the electron beam travels along said lines without undesirable transverse pulsations.
 2. An electron-beam genenrator as claimed in claim 1, wherein said thermionic emitter, cathode, anode and additional electrode are toroidal bodies of revolution disposed concentrically and said electromagnetic system is cylindrical and wherein said lines of force of the magnetic field formed by the cylindrical electromagnetic system means coaxial with said emitter lie in meridian planes.
 3. An electron beam generator as claimed in claim 1, wherein said magnetic field includes parallel magnetic field lines, and said thermionic emitter has a rectilinear elongated configuration, and said cathode, anode and additional electrode have cylindrical surfaces whose generatrices thereof are parallel to said emitter and perpendicular to a plane containing the lines of force of said magnetic field lines established by said electromagnetic system means disposed in the same direction as the emitter.
 4. An electron-beam generator as claimed in claim 1, wherein said emitter is formed as a curvilinear rod, and said cathode, anode, additional electrode and electromagnetic system means have curved shapes in conformity with the curvature of said emitter.
 5. An electron-beam generator as claimed in claim 1, wherein said electromagnetic system means is provided with a soft-iron shield.
 6. An electron-beam generator as claimed in claim 1, wherein said anode is disposed on one side of said emitter.
 7. An electron-beam generator as claimed in claim 1, comprising an additional conductive rod means maintained at a potential the same as that of said anode so as to form an emission chamber confined on two sides thereof in a traNsverse direction of said rod.
 8. An electron-beam generator as claimed in claim 1, wherein said thermionic emitter includes an active surface located in a direction opposite to a direction of movement of the accelerated electron beam. 